Explanation

The pattern followed here is:

1) 25631→ 2 + 5 + 6 + 3 + 1 = 17

2) 33442 → 3 + 3 + 4 + 4 + 2 = 16 (Not follow the pattern)

3) 34424 → 3 + 4 + 4 + 2 + 4 = 17 4) 52163 → 5 + 2 + 1 + 6 + 3 = 17

Hence, '33442' is the correct answer.